The present invention relates to composite gun barrels for small arms, and in particular, to a gun barrel for small arms wherein the gun barrel is made with a composite portion and a metallic portion formed so that the coefficient of expansion of the composite is contrasted in the radial direction relative to that of the metal portion of the gun barrel and has 0 or nearly 0 coefficient of thermal expansion in the axial direction so as to achieve desiring firing characteristics for the gun barrel.
The use of composite/metallic gun barrels is well known in the art of weapons manufacturing. Typically, composite/metallic gun barrels are made from thin-walled cylinders of metal which are overlaid with a composite material. The composite layer provides increased strength and stiffness to the gun barrel, while simultaneously reducing the weight of the barrel. Thus, a gun simultaneously can be made lighter, stronger and stiffer by not using a conventional metallic barrel.
In most attempts to replace the conventional barrel, however, a thin metallic barrel liner is used. Typically, the metallic portion of the barrel will be less than one-tenth of an inch thick along most of the length of the barrel. The metallic liner serves two major purposes. First, the metallic barrel liner provides a hard, machinable surface for spiral riflings in the liner bore which provide a rotational spin to the bullet during flight and greatly improves accuracy. In contrast, a composite material is not sufficiently hard, is friable, and is otherwise unsuitable for barrel riflings. Second, the metallic barrel liner is used to shield the composite material from the hot, corrosive gasses generated when firing a bullet. As the powder burns to propel the bullet through the barrel, the hot gasses formed by the burning powder to propel the bullet contact the barrel. Those skilled in the art will appreciate that such gasses can weaken the composite material under certain circumstances.
One problem which has developed with barrels having a metallic liner surrounded by composite is that they often fail to operate as desired when repeatedly fired. As a gun is fired several times in rapid succession, the heat generated from the firing of each bullet begins to accumulate in the barrel. Because the metal liner and the composite materials generally have somewhat different coefficients of expansion when exposed to heat, a barrel heated by repeated firing can quickly loose its accuracy and consistency. This is due in large part to prior art lack of awareness and/or inability to form composite/metallic gun barrels, wherein the coefficients of thermal expansion are correlated to the desired use of the barrel.
In apparent attempts to overcome such problems of the prior art, the present level of skill in the art teaches that it is best to select a metallic liner having a coefficient of thermal expansion in the radial direction which matches the expansion coefficient of the composite being used in the radial direction. This involves the process of first identifying the coefficient of thermal expansion for the composite and then selecting amid a limited number of suitable metals to try and match that same coefficient of thermal expansion. However, as will be appreciated by those skilled in the art, the search for such a combination of a specific metallic liner with a similar expansion coefficient to a composite material may not provide the desired characteristics in other areas, such as strength and durability.
Thus, there is a need for a composite/metallic barrel which is formed so that the composite, the metal and their expansion coefficients provide desired characteristics during firing. For example, when such barrel is used for a gun which rapidly fires rounds and in which accuracy is of less concern, such as a military machine gun, superior gun performance is achieved by having the composite/metallic barrel wherein the coefficients of thermal expansion are contrasted so the composite restricts expansion of the metallic barrel and prevents bullets from excessive wobbling as they pass down the barrel. While other composite/metallic barrels may inadvertently constrict on the barrel, they do so unevenly, thereby increasing frictional wear by each bullet.